Layer Variations of Long-Term Depression in Rat Visual Cortex

Department of Ophthalmology and Visual Science, Yale University School of Medicine, New Haven, Connecticut 06520 Submitted 24 March 2004; accepted in final form 17 June 2004 In vitro long-term depression (LTD) is thought to be a model for the loss of cortical responsiveness to an eye deprived of vision during the critical period. Using whole cell recording, the present study investigates the mechanisms of LTD in vitro across layers in developing rat visual cortex. LTD was induced in layers II/III, V, and VI but not layer IV with 10-min 1-Hz stimulation paired with postsynaptic depolarization. LTD in layers II/III and V could be blocked by the N -methyl- D -aspartate (NMDA) receptor antagonist D -aminophosphonovaleric acid ( D -AP5) but not by 100 µM (2S)-amino-2-[(1S,2S)-2-carboxycycloprop-1-yl]-3-(xanth-9-yl) propanoic acid (LY341495 ), a metabotropic glutamate receptor inhibitor. In contrast, LTD in layer VI was blocked by 100 µM LY341495 and (RS)-1-aminoindan-1,5-dicarboxylic acid (AIDA) but not D -AP5 and partially blocked by application of guanosine 5'- O -(2-thiodiphosphate) thilothium salt (GDP- -S) in patch pipette, suggesting an involvement of postsynaptic group I metabotropic glutamate receptors (mGluRs). These results indicate that LTD in developing rat visual cortex varies with layer: LTD was absent in layer IV, suggesting a unique plasticity mechanism at geniculocortical synapses; LTD in layers II/III and V depends on NMDA receptors but not mGluRs, and LTD in layer VI requires mGluRs but not NMDA receptors. Address for reprint requests and other correspondence: Y. Rao, Dept. of Ophthalmology and Visual Science, Yale University Medical School, 330 Cedar St., New Haven, CT 06520-8061 (E-mail: yan.rao{at}yale.edu ).